1. Field of the Invention
This invention relates to sealing, packing, and valve systems used in subterranean oil and gas wells for providing an annular seal between a fluid transmission conduit disposed in another conduit or casing, and allowing one-way flow in the annulus to permit injection of treating fluids through the tubing-casing annulus.
2. Description of the Prior Art
There are many different downhole tools in the oil and gas industry which require that a seal be established in the annulus between a fluid transmission conduit or tubing string disposed in a well bore and the outer well casing. These tools may relate to the drilling and completion of the well, the production of the well, the servicing of the well, or the abandonment of the well. Conventional packers, employing an anchoring system for holding a sealing element in position against either upwardly or downwardly acting pressure differentials, are most often employed for establishing this seal. These conventional packers generally employ radially expandable anchor slip systems and radially expandable packing or sealing elements to prevent fluid communication and to provide pressure integrity. Such packers are typically run in and set in place either by or on a tubing string or a wireline setting tool. The packer is typically set using hydraulic pressure in the tubing, hydrostatic pressure in the well bore, tension applied through the tubing string, or a combination. It may also be mechanically set by the weight of the tubing. These packers can be permanent type packers with an internal seal bore for receiving tubing which can be retrieved while leaving the packer in place. Retrievable packers, employing techniques such as rotary manipulation of the tubing string to release anchor slip assemblies and packing elements for retrieval of the packer are also commonly employed.
In addition to the use of conventional packing elements to provide sealing integrity in the tubing casing annulus and to isolate the production zone from portions of the annulus extending above the packing element, casing polished bore receptacles have been employed in conjunction with sealing elements to achieve some of the objectives achieved by conventional packers. A typical prior art example of the use of packoff assemblies in conjunction with casing bore receptacles or liners is discussed on pages 6438 and 6439 of the 1978-79 Composite Catalog of Oil Field Equipment and Services published by World Oil.
It is generally necessary that sealing integrity be established between separate elements within the tubing string or between accessory items and the tubing string. For example, it is generally necessary that tubing sections, inserted into a seal bore of a packer, must have sealing integrity between that section and the packer. One means of providing such sealing integrity is to utilize stacks of sealing elements in which individual sealing elements have a generally chevron-shaped cross section. Sealing systems employing such chevron-shaped sealing elements are depicted on page 672 of the 1980-81 Composite Catalog of Oil Field Equipment and Services published by World Oil. These chevron-shaped sealing elements and systems, commonly referred to as tubing seal systems, could be employed to establish a seal between a tubing mounted element and the internal seal bore of a conventional packer. An alternative method of establishing a seal between a conventional packer and tubing elements while still permitting movement of the tubing elements relative to the packer is depicted in U.S. Pat. No. 3,109,490 covering a slidable latching seal assembly.
The present invention uses a casing bore receptacle concept and can employ conventional tubing seals to provide the seal between the tubing and the casing.
A seal assembly comprising a casing bore receptacle, an annular packoff member, and further comprising a radially expandable latch, and a reciprocal mandrel member is disclosed and claimed in my co-pending application entitled "Casing Bore Receptacle" filed 6-16-81.
In addition to providing a seal in the annulus between a fluid transmission conduit and an exterior conduit, it is often desirable to permit the injection of fluids into the annulus between the tubing and the casing. Such injection may be especially desirable in offshore wells where a treating fluid, such as a corrosion inhibitor or a kill fluid, is injected into the annulus to protect the tubing and the casing from highly corrosive produced hydrocarbons. It would be desirable to use tubing having the largest possible diameter to provide for the greatest possible production while, at the same time, providing for the injection of corrosion inhibitors and their circulation throughout the tubing and the casing. Due to the complex construction of packers it is difficult to incorporate both a passageway through the packer having a bore equivalent to that in the tubing and a valve mechanism having the capacity to permit the injection of a sufficient volume of corrosion inhibitor or kill fluid. The difficulty of achieving these objectives in one device based on a conventional packer is compounded where the available cross-sectional area between the tubing and the casing is limited.
One solution which has previously been suggested is to provide a polished bore receptacle along the casing in conjunction with a check valve located within the annulus. Such an arrangement will permit fluid to pass through the check valve, with the injected fluid passing therethrough down into those sections where the diameter of the well may be less, and subsequently into the tubing, and then up with the produced hydrocarbons through the tubing to the surface of the well. Latching means can also be employed in conjunction with the polished bore receptacle, the check valve, and tubing hangers located in the vicinity of the check valve.
The present invention provides a unique means of incorporating a check valve in an annular packoff assembly to allow both the injection of treatment fluids, such as corrosion inhibiting fluids, from above and to provide for adequately sealing the annulus in response to pressures existing in the annulus below the packoff member. In this way, the produced hydrocarbons cannot flow up through the tubing-casing annulus, but corrosion inhibiting fluids and solutions can flow down through the annulus to protect both the tubing and the casing over their entire length.